The present invention relates to a three-piece type optical lens, and more particularly to an optical lens for mobile phones or image sensors such as CCD (Charge Coupled Device) or CMOS (Complementary Metal. Oxide Semiconductor) formed by three pieces of lens with features of high performance, minimized total length and low cost.
Due to fast development of modern technology, electronics have become compact with more functions. A lot of electronics such as digital still cameras, PC (personal computer) cameras, network cameras, mobile phones, even personal digital assistants are equipped with image capturing devices (lens). For convenience of easy-carrying and requirement of humanization, the image capturing devices requires good image quality, compact volume and low cost. Especially for applications on mobile phones, the above requirements are getting more important.
Owing to various materials available for making the lens and better correcting effect for color aberration, conventional spherical ground glass lenses have been widely adopted in optical industry field. However, the spherical ground glass lenses have poor effect on correction of spherical aberration and astigmatic aberration when being applied under condition of a smaller F number and wide angle of field. To improve above shortcomings of the conventional spherical ground glass lenses, the image capturing devices available now use aspherical plastic lenses or aspherical molded glass lenses to replace conventional spherical ground glass lenses for better imaging quality. For example, refer to the lenses disclosed in U.S. Pat. No. 6,795,253, U.S. Pat. No. 6,961,191 U.S. Pat. No. 6,441,971, Pub. No. US 2004/0061953 A1, Pub. No. US 2004/0190158 A1, Pub. No. US 2004/0190162 A1, Pub. No. US 2004/0231823 A1, Pub. No. US 2005/0231822 A1, or Japanese patent No. 3567327, No. 3717488, No. 3768509, No. 3816095, Pub. No. 2005-084404, Pub. No. 2006-047858, Pub. No. 2005-309210, Pub. No. 2005-227755, Pub. No. 2005-345919, Pub. No. 2005-292235, Pub. No. 2004-004566, Pub. No. 2005-338234 are all composed of three lens components/lens elements—a first lens element, a second lens element and a third lens element arranged in order from the object side. Basic design of above patents are composed of a first, a second and a third lens set/lens element in order from the object side. The differences among embodiments of above patents are in components or combinations of components. Or the design of the first, the second and the third lens sets/lens elements are in different shapes. For example, the three lens sets/lens elements are all in meniscus shape or the first and the second lens sets/lens elements are meniscus while the third lens set/lens element is in plano-concave shape or plano-convex shape. Or the convex surface/concave surface of the first/second/third lens sets/lens elements can be arranged on the object/image side. Or the refractive power of the three lens sets/lens elements may vary. For example, refractive power of the first the second and the third lens sets/lens elements are respectively positive, negative, positive or positive positive, negative in sequence. The three lens set/lens element respectively satisfy various optical parameters such as f (effective focal length of the whole optical lens), d (distance between the object side of the first lens element and the image side of the third lens element), R1 (radius of curvature of the object side of the first lens element), R2 (radius of curvature of the image side of the first lens element), Fno (F number of the optical lens), br (back focal length of the whole optical lens), f1 (effective focal length of the first lens element), and f3 (effective focal length of the third lens element). For example, refer to Japanese patent No. 3717488, the conditions of: 0.8<f1/f<2.0, 0.5<(|R2|−R1)/(R1+|R2|), and 1.5<f3/f<3.0 are satisfied.
Thus it is learned the design of a three-piece type optical lens is not so difficult in this field. However, total lens of the above optical lens is still too long so that the optical lens can't have smaller volume with lower cost. Moreover, correction effect of aberration of the lens as well as light angle is not ideal. Thus general requirement of electronic products such as compact and good performance can't be achieved. Therefore, applications of the optical lens are limited, especially unable to be applied to mobile phones.